1. Field of the Invention
This invention relates in general to a refrigerant cycling device, for example, a transcritical refrigerant cycling device, wherein a compressor, a gas cooler, a throttling means and an evaporator are connected in sequence, and a hyper critical pressure is generated at a high pressure side. In addition, the present invention relates to a refrigerant cycling device using a multi-stage compression type compressor.
2. Description of Related Art
In a conventional refrigerant cycling device, a rotary compressor (compressor), a gas cooler, a throttling means (such as an expansion valve), are circularly connected with pipes in sequence, so as to construct a refrigerant cycle (a refrigerant cycling loop). The refrigerant gas is absorbed from an absorption port of a rotary compression element of the rotary compressor into a low pressure chamber of a cylinder. By an operation of a roller and a valve, the refrigerant gas is compressed to a high temperature and high pressure refrigerant gas. The high temperature and high pressure refrigerant gas passes through a discharging port, a discharging muffler chamber, and then is discharged to the gas cooler. After the refrigerant gas releases heat at the gas cooler, the refrigerant gas is throttled by the throttling means and then supplied to the evaporator. The refrigerant gas is evaporated by the evaporator. At this time, heat is absorbed from the ambience to achieve a cooling effect.
For addressing earth environment issues, this kind of refrigerant cycling loop also begins to use a nature refrigerant, such as carbon dioxide (CO2), rather than use a conventional Freon refrigerant. A device using a transcritical cycle where the high pressure side is operated as a hyper critical pressure is developed.
In such a transcritical cycling device, liquid refrigerant will return back to the compressor. For preventing a liquid compression, a receiver tank is arranged at a low pressure side between an outlet of the evaporator and an absorption side of the compressor. The liquid refrigerant is thus accumulated at the receiver tank, and only the gas is absorbed into the compressor. Referring to Japanese Laid Open Publication H07-18602, the throttling means is adjusted so that the liquid refrigerant in the receiver tank will not return back to the compressor.
However, a large amount of refrigerant has to be filled for installing the receiver tank at the low pressure side of the refrigerant cycle. In addition, an aperture of the throttling means has to be reduced for preventing a liquid back effect; otherwise, the capacity of the receiver tank has to be increased. That will cause a reduction of the cooling ability and an enlargement of an installation space. For solving the liquid compression in the compressor without using the receiver tank, the present inventors develop a conventional refrigerant cycling device as shown in FIG. 18.
Referring to FIG. 18, an internal intermediate pressure multi-stage (two stages) rotary compressor 10 comprises an electric motor element (a driving element) 14 in a sealed container 12, a first rotary compression element 32 and a second rotary compression element 34 both of which are driven by a rotational shaft 16 of the electric motor element 14.
The operation of the aforementioned refrigerant cycling device is described as follows. The refrigerant absorbed from a refrigerant introduction pipe 94 of the compressor 10 is compressed by the first rotary compression element 32 to possess an intermediate pressure, and then is discharged from the sealed container 12. Afterwards, the refrigerant comes out of the refrigerant introduction pipe 92 and flows into an intermediate cooling loop 150A. The intermediate cooling loop 150A is arranged to pass through a gas cooler 154, so that heat is radiated in an air cooling manner at the intermediate cooling loop 150A and heat of the intermediate pressure is taken by the gas cooler 154.
Thereafter, the refrigerant is absorbed into the second rotary compression element 34 and the second stage compression is performed, so that the refrigerant gas becomes high pressure and high pressure. At this time, the refrigerant is compressed to have a suitable hyper critical pressure.
After the refrigerant gas discharged from a refrigerant discharging pipe 96 flows into the gas cooler 154 and radiated in an air cooling manner, the refrigerant gas passes through an internal heat exchanger 160. Heat of the refrigerant is taken at the internal heat exchanger 160 by the refrigerant coming out of the evaporator 157 and thus is further cooled. Then, the refrigerant is depressurized by an expansion valve 156, and becomes gas/liquid mixed status during that process. Next, the refrigerant flows into the evaporator 157 and evaporates. The refrigerant coming out of the evaporator 157 passes through the internal heat exchanger 160, and takes heat from the refrigerant of the high pressure side so as to be heated.
The refrigerant heated by the internal heat exchanger 160 is then absorbed from the refrigerant introduction pipe 94 into the first rotary compression element 32 of the rotary compressor 10. In the refrigerant cycling loop, the aforementioned cycle is repeated.
In the transcritical refrigerant cycling device as described above in FIG. 18, the refrigerant can possess an overheat degree in a manner that the refrigerant coming out of the evaporator 157 is heated by the refrigerant of the high pressure side by using the internal heat exchanger 160. Therefore, the receiver tank at the low pressure side can be abolished. However, since redundant refrigerant may occur due to a certain operation condition, a liquid back effect in the compressor 10 will arise and a damage caused by the liquid compression might be occur.
In addition, in the aforementioned transcritical refrigerant cycling device, if an evaporation temperature at the evaporator reaches a low temperature range of −30° C. to −40° C. or an extremely low temperature range equal to or less than −50° C., the compression ratio will become very high. Therefore, it is very difficult to achieve the above temperature range because the temperature of the compressor 10 itself becomes very high.
Furthermore, Japanese patent No. 2507047 discloses a refrigerant cycling device using an internal intermediate pressure multi-stage (two stages) rotary compressor. In the refrigerant cycling device, the intermediate pressure refrigerant gas in the sealed container is absorbed from the absorption port of the second rotary compression element to the low pressure chamber of the cylinder. By the operation of the roller and the valve, the second stage compression is performed and thus the refrigerant becomes high temperature and high pressure. From the high pressure chamber and passing through the discharging port and the discharging muffler chamber, the refrigerant is discharged to the exterior of the compressor. Thereafter, the refrigerant enters the gas cooler for radiating heat to achieve a heating effect, and then the refrigerant is throttled by an expansion valve (as the throttling means) to enter the evaporator. After the refrigerant absorbs heat to evaporate at the evaporator, the refrigerant is absorbed into the first rotary compression element. The aforementioned cycle is repeated.
However, in the refrigerant cycling device using the above compressor, if there is a pressure difference of the rotary compression element when restarting after the compressor stops, the start ability will degrade and damage will be caused. In order to equalize the pressure in the refrigerant cycling loop early after the compressor stops, there is a situation that the expansion valve is fully open to connect the low pressure side and the high pressure side. However, the low pressure side and the high pressure side does not connect to each other after the compressor stops, the intermediate pressure refrigerant gas in the sealed container, which is compressed by the first rotary compression element, needs time to achieve an equilibrium pressure.
In addition, since the heat capacitance of the compressor is large, the temperature reducing speed is very slow. After the compressor stops operating, the temperature in the compressor might be higher than the other portion of the refrigerant cycling loop. Moreover, in a case that the refrigerant immerses into the compressor (the refrigerant is liquidized) after the compressor stops, an intermediate pressure is suddenly increased since the refrigerant becomes a flash gas immediately after the compressor starts. Therefore, the pressure of the intermediate pressure refrigerant gas in the sealed container is conversely higher than a pressure at the discharging side (the high pressure side in the refrigerant cycling loop) of the second rotary compression element; namely, a so-called pressure inversion phenomenon occurs. In this case, the pressure behavior when the compressor starts is described according to FIGS. 19 and 20. FIG. 19 is a conventional diagram of a pressure behavior when the compressor starts normally. Since the pressure in the refrigerant cycling device reaches an equilibrium pressure before the compressor starts, the compressor can start as usually, so that a pressure inversion between the intermediate pressure and the high pressure will not occur.
On the other hand, FIG. 20 shows a pressure behavior when the pressure inversion phenomenon occurs. As shown in FIG. 20, the low pressure and the high pressure are equalized (solid line) before the compressor starts. However, as described above, when the compressor starts, the intermediate pressure becomes higher than the equalized pressure (dash line), and thus, the intermediate pressure increases much more and becomes as high as or higher than the high pressure.
Particularly, in the rotary compressor, since a valve of the second rotary compressor element is energized to a roller side, the pressure at the discharging side of the second rotary compression element acts as a back pressure. However, in that case, since the pressure at the discharging side of the second rotary compression element (the high pressure) is the same as the pressure at the absorption side of the second rotary compression element (the intermediate pressure) or the pressure at the absorption side of the second rotary compression element (the intermediate pressure) is higher, the back pressure that the valve energies to the roller will not act and thus the valve of the second rotary compression element might fly. Therefore, the compression of the second rotary compression element is not performed and in fact, only the compression of the first rotary compression element is performed.
In addition, for the valve of the first rotary compression element, since the valve is energized to the roller, the intermediate pressure in the sealed container acts as a back pressure. However, as the pressure in the sealed container increases, a pressure difference between the pressure in the cylinder of the first rotary compression element and the pressure in the sealed container is too large, and a force that valve presses to the roller has to be increased. Therefore, a surface pressure acts obviously on a sliding portion between the front end of the valve and the outer circumference of the roller, so that the valve and the roller are worn to cause a dangerous damage.
On the other hand, as described above, in the case that the intermediate pressure compressed by the first rotary compression element is cooled by the intermediate heat exchanger, due to a certain operation condition the temperature of the high pressure refrigerant compressed by the second rotary compression element may not satisfy a desired temperature.
Particularly, when the compressor starts, the temperature of the refrigerant is very difficult to increase. In addition, there is also a situation that the refrigerant gas immerses into the compressor (liquidization). In this case, it needs that the temperature inside the compressor can rise early to return the normal operation. However, as described above, in the case that the refrigerant compressed by the first rotary compression element is cooled by the intermediate heat exchanger and absorbed into the second rotary compression element, it is very difficult to rise the temperature in the compressor early.
Furthermore, in the aforementioned compressor, an opening at the upper side of the second rotary compression element is blocked by a supporting member, and another opening at the lower side is blocked by an intermediate partition plate. A roller is disposed in the cylinder of the second rotary compression element. The roller is embedded to an eccentric part of the rotational shaft. For preventing from wearing the roller between the roller and the aforementioned supporting member arranged at the upper side of the roller as well as between the roller and the aforementioned intermediate partition plate arranged at the lower side of the roller, a tiny gap is formed. As a result, the high pressure refrigerant gas compressed by the cylinder of the second rotary compression element might flow from the gap to the inner side of the roller, so that the high pressure refrigerant gas will accumulate at the inner side of the roller.
As mentioned above, as the high pressure refrigerant accumulates at the inner side of the roller, since the pressure at the inner side of the roller becomes higher than the pressure (the intermediate pressure) of the sealed container whose bottom servers as an oil accumulator, it is very difficult to utilize a pressure difference to supply the oil from the oil supplying hole to the inner side of the roller through an oil hole of the rotational shaft, causing an insufficient oil supplying amount to the peripheral of the eccentric part of the inner side of the roller. Conventionally, as shown in FIG. 21, a passage 200 for connecting the inner side (the eccentric part side) of the roller of the second rotary compression element and the sealed container is arranged in the upper supporting member 201 that is arranged at the upper side of the cylinder of the second rotary compression element. Therefore, the high pressure refrigerant gas accumulated at the inner side of the roller will be released into the sealed container, so as to prevent the inner side of the roller from becoming a high pressure.
However, for forming the aforementioned passage 200 that connects the inner side of the roller and the interior of the sealed container, it has to form two passages 200A, 200B, wherein the passage 200A is formed in an axial direction by drilling a hole at the inner side of the roller at the inner circumference of the upper supporting member, and the passage 200B is formed in the horizontal direction for connecting the passage 200A and the sealed container. Therefore, the processing work for forming the passages increases, and thus its corresponding manufacturing cost also increases.
On the other hand, since the pressure (the high pressure) in the cylinder of the second rotary compression element is higher than the pressure (the intermediate pressure) in the sealed container whose bottom servers as the oil accumulator, it is very difficult to utilize a pressure difference to supply the oil from the oil supplying hole or the oil hole of the rotational shaft to the interior of the cylinder of the second rotary compression element. By only using the oil melted into the absorbed refrigerant to lubricate, there might be a problem of insufficient oil supplying amount.
Moreover, in the aforementioned rotary compressor, the refrigerant gas compressed by the second rotary compression element is directly discharged to the exterior. However, the aforementioned oil supplied to a sliding part inside the second rotary compression element is mixed with the refrigerant gas, and then, the oil is discharged to the exterior together with the refrigerant gas. Therefore, the oil in the oil accumulator inside the sealed container becomes insufficient, so that a lubrication ability for the sliding part degrades and the ability of the refrigerant cycling loop degrades because a large amount of oil flows to the refrigerant cycling loop. In addition, for preventing the above problem, if the oil supplying amount to the second rotary compression element is reduced, there will be a problem in a circularity of the sliding part of the second rotary compression element.